Thin plates are one of the efficient structural systems of lightweight structures. A thin plate is highly flexible under out-of-plane loading and extremely stiff under in-plane loading. In-plane strength of a plate is always greater than the buckling strength and the load carried by the plate beyond the buckling load is due to the out-of-plane stiffness. The provision of stiffeners increases the out-of-plane stiffness of the plate without causing significant change in self-weight of the plate. Fiber reinforced polymer (FRP) is a versatile composite material widely used in aerospace and automotive sectors. Corrosion resistance and durability properties of FRP gained the acceptance in civil engineering structures such as bridge decks, box girder bridges, offshore oil platforms and ship structures. Stiffened plates used in the decks of ship and offshore oil platforms are predominantly subjected to in-plane and out-of-plane loads. The presence of openings in the stiffened plates for providing access reduces the load allowed on the plate. The present study mainly focuses the investigation of load-deflection behavior and ultimate load on the FRP stiffened plates with multiple panels. Materials used for the fabrication of stiffened FRP plates will be characterized as per ISO/ASTM standards to obtain the strength and stiffness properties. The experimental investigation will be carried out on eight FRP stiffened composite specimens of size 1 m x 3 m with 6 flat stiffeners cast integrally by hand lay-up process with and without openings under in-plane, out-of-plane and combined loading. Initial geometric imperfections that influence the ultimate strength of the stiffened plates will be measured prior to the testing. ABAQUS CAE is used to develop finite element model for the correlation of load-deflection behavior considering the data available from the material characterization and imperfection measurement. Hashin’s failure criteria is used in the model for defining the failure of the composites. The reduction in the ultimate load of the specimens due to the presence of openings will be found by both numerically and experimentally. Further parametric studies will be carried out with different geometry of the plate, size of openings and reinforcement around the opening to provide the guidelines for the design.
Keywords: stiffened composite plate, FRP composite, buckling, out-of-plane load, in-plane load, multiple panel, flat stiffener, hand lay-up process, geometric imperfection.